等渗溶液Ca2＋浓度改变对去神经主动脉平滑肌生物张力及兴奋性作用研究

Denervated aortic smooth muscle tension and cellular membrane current in variations of calcium ion concentration in iso-osmotic solution

目的研究等渗高Ca2＋环境对去神经主动脉平滑肌膜电流的影响，以及不同前负荷状态和Ca2＋通道阻滞剂干预下去神经主动脉平滑肌的肌源性自主舒缩变化。方法平滑肌标本取自昆明小鼠主动脉平滑肌层。标本在松弛状态下被两端固定并浸润于任氏液中，待稳定后于显微镜下将玻璃微电极吸附于平滑肌肌膜并高阻封接，观察生理渗透压环境下的膜电流状态。将任氏液中Ca2＋浓度由0．9mol／L提高至1．2mol／L，观察渗透压改变后的即刻膜电流变化。增加标本前负荷至1g，观察前负荷增加后标本在同等渗透压环境下膜电位的改变，并记录此时的标本自主舒缩曲线。结果平滑肌标本处于松弛状态时，在等渗环境下将Ca2＋浓度由0．9mol／L提高至1．2mol／L后，膜电流改变幅度由（10．25±1．34）pA增至（24．91±3．27）pA，差异具有统计学意义（P〈0．05）；前负荷增加后标本在等渗高ca“及低ca“环境下的膜电流改变幅度较松弛状态时均有所增加（低Ca2＋浓度时（15．33±4．33）pA比（10．25±1．34）pA，高Ca2＋浓度时（33．31±7．25）pA比（24．91±3．27）pA），差异均具有统计学意义（均P〈0．05）。低Ca2＋浓度为0．9mol／L时，若仅增加前负荷，标本肌源性自主舒缩幅度可增加175％；而Ca2＋浓度增至1．2mol／L时，标本自主舒缩幅度可进一步增长40％。经Ca2＋通道阻滞剂（质量浓度为0．5g／L尼群地平）预处理后，高Ca2＋环境下的膜电流及肌源性th主舒缩均明显减弱，结果表明膜电位及自主舒缩均由Ca2＋主导。结论细胞外Ca2＋浓度的增加既提高了主动脉平滑肌细胞膜的兴奋性，又使平滑肌产生较明显的自主性舒缩，可在前负荷改变时有效地改善平滑肌组织顺应性。Ca2＋百道阻滞剂抑制了Ca2＋主导的跨膜电流，降低了肌源性自主舒缩，增加了平滑肌的僵直度，这可能会对改善弹性储器血管的功能产生负面影响。

Objective To study the influence of high calcium ion environment on the membrane current of denervated aortic smooth muscles in iso-osmotic condition, as well as study the myogenic spontaneous vasomotion of the aortic smooth muscles under different pre-load state and intervention of calcium-channel blockers. Methods Smooth muscle samples were taken from the aortic smooth muscle layer of Kunming mice. The samples were fixed at two-ends in relaxed state and infiltrated in Ringer＇s solution. After stabilization, a glass microelectrode was adsorbed on the smooth muscle membrane to form gigaohm-seal. The current state of the membrane was observed under the physiological osmotic pressure. Then, the calcium ions concentration in the Ringer＇s solution was increased from 0.9 mol/L to 1.2 mol/L, and the immediate change of membrane current was observed after changing of osmotic pressure. Finally, the membrane potential change in iso-osmotic condition was observed when the pre-load was increased to 1 g, and the spontaneous vasomotion curves of the samples were recorded. Results In the relaxation state, the membrane current of the smooth muscle was increased significantly, i.e. （10.25 ±1.34） pA vs. （24.91±3.27） pA （P〈0.05）, when the calcium ion concentration was increased from 0.9 mol/L to 1.2 mol/L in iso-osmotic condition. When the pre-load was increased, the variation amplitude of the membrane current was increased in iso-osmotic condition, i.e. （10.25±1.34） pA to （15.33±4.33） pA （P〈0.05） for the lower calcium ion concentration, and （24.91±3.27） pA to （33.31±7.25） pA （P〈0.05） for the higher calcium ion concentration. If only increasing the pre-load, the myogenic spontaneous vasomotion could be increased by 175% for the condition of lower calcium ion concentration （0.9 mol/L）. When the calcium ion concentration was increased to 1.2 mol/L, the spontaneous vasomotion frequency of the specimen was increased, and the range of the vasomotion could be further increased by 40%. After pretreatment with the calcium-channel blocker （0.5 g/L nitrendipine）, the membrane current and myogenic spontaneous vasomotion were significantly decreased in the higher calcium ion environment, which indicated that the membrane potential and spontaneous vasomotion was dominated by calcium ions. Conclusions The increase of extracellular calcium ion concentration not only can improve the excitability of the aorta smooth muscle cells, but also can cause significant spontaneous vasomotion, and can improve the compliance of the smooth muscle tissue in pre-load variation. The calcium-channel blockers can inhibit calcium-dominated transmembrane currents, reduce myogenic spontaneous vasomotion, and enhance the stiffness of smooth muscle, which may have negative effects on windkessel vessel function.